Wash potatoes. Peel half of them (some skins will be left on). Chop into 3/4-inch pieces. Boil until can be pierced with a fork, about 20 minutes. Remove from heat and drain. Stir potatoes. Some should mash, and some pieces should remain solid. Mix in mayonnaise and mustard.
Alternate version: Two chopped hard-boiled eggs may be added, if desired.
Ensalada de papas may be served warm or cold.

(This recipe was contributed as part of a "Cook of the Week" feature.)